This invention relates generally to apparatus and a method for protecting beaches and shorelines and more particularly apparatus and a method for preventing erosion of beaches and shorelines by wave action and for building up such beaches and shorelines by sedimentation of water suspended particles.
As a result of coastal evolution, storm waves, and a general rise in sea level, shoreline recession has become a widespread phenomenon throughout the world. A common response to the dynamic waterfront erosion process normally involves implementing some type of shoreline stabilization process ranging from the simple planting of dune grass or other vegetation to the complex construction of large sea walls, offshore breakwaters, groins or jetties. Unfortunately, the construction costs inherent in stabilizing shorelines using such conventional techniques are high, while the benefits derived therefrom are often shortlived.
As will be appreciated by those skilled in the art, a beach or shoreland is one of nature's most dynamic environments, with a zone of active sand movement constantly changing and ever migrating in accordance with natural law. The dynamic equilibrium of all shoreline systems depends on wave size, sea level rise, beach sand supply, the shape of the beach, as well as the impact of human beings on the system. Beaches are created during periods of good weather and are eroded during storm tides.
Waves travel by pressure and move in an oscillating fashion somewhat similar to stalks of grain swaying in the wind. The forward and backward motions of the water, moving just above the bottom of the sea, are unsymmetrical, with the forward motion being stronger and of shorter duration than the backward motion. The carrying capacity for suspended solids in the moving water is generally proportional to the velocity of the flow. That velocity of flow can be regulated or influenced by environmental and/or man-made barriers. Thus, when the velocity of the flow is sufficiently reduced, deposition of suspended solid matter occurs.
The best protection against shoreline erosion is a wide beach since that environment causes the waves to break, thereby dissipating the wave energy before the erosion of the shoreline can occur. Normally, beaches grow seaward by deposition of sand from longshore currents and new sand brought from offshore by the formation of a ridge and runnel system perpendicular to the beach. Long waves of small amplitude serve to replenish the shoreline, while short storm waves of high amplitude erode the shoreline.
Experience has shown that natural sandbars provide excellent protection against destructive wave forces. Consequently, attempts have been made to simulate sandbar action by constructing artificial barriers parallel to the shoreline. Such barriers have been unsuccessful because high velocity water currents typically scour and undermine their foundations, causing the barriers to fail and to lose their effectiveness.
Some prior art patents have disclosed methods and/or apparatus for controlling the erosion of shoreline. Examples of such patents are U.S. Pat. Nos. 3,564,853 (Csiszar), 3,214,916 (Martin), 2,655,790 (Daley), 1,969,123 (Doble) and 226,772 (Meuller). While the systems of the foregoing patents may, to some extent, be effective for controlling erosion of shorelines or aiding in building up beaches, they nevertheless suffer from one or more of various drawbacks, such as complexity, cost, effectiveness and longevity.